The present invention relates to interconnection structure and method for forming the same in a semiconductor integrated circuit.
As the number of devices, integrated within a single semiconductor integrated circuit, has been tremendously increasing these days, wiring delay has also increasing noticeably. This is because the larger the number of devices integrated, the larger line-to-line capacitance (i.e., parasitic capacitance between metal interconnects), thus interfering with the performance improvement of a semiconductor integrated circuit. The wiring delay is so-called xe2x80x9cRC delayxe2x80x9d, which is proportional to the product of the resistance of metal interconnection and the line-to-line capacitance.
In other words, to reduce the wiring delay, either the resistance of metal interconnection or the line-to-line capacitance should be reduced.
In order to reduce the interconnection resistance, IBM Corp., Motorola, Inc., etc. have reported semiconductor integrated circuits using copper, not aluminum alloy, as a material for metal interconnects. A copper material has a specific resistance about two-thirds as high as that of an aluminum alloy material. Accordingly, in accordance with simple calculation, the wiring delay involved with the use of a copper material for metal interconnects can be about two-thirds of that involved with the use of an aluminum alloy material therefor. That is to say, the operating speed can be increased by about 1.5 times.
However, the number of devices, integrated within a single semiconductor integrated circuit, will certainly continue to increase by leaps and bounds from now on, thus further increasing the wiring delay considerably. Therefore, it is concerned that even the use of copper as an alternate metal interconnection material would not be able to catch up with such drastic increase. Also, the specific resistance of copper as a metal interconnection material is just a little bit higher than, but almost equal to, that of gold or silver. Accordingly, even if gold or silver is used instead of copper as a metal interconnection material, the wiring delay can be reduced only slightly.
Under these circumstances, not only reducing interconnection resistance but also suppressing line-to-line capacitance play a key role in further increasing the number of devices that can be integrated within a single semiconductor integrated circuit. And the relative dielectric constant of an interlevel insulating film should be reduced to suppress the line-to-line capacitance. A silicon dioxide film has heretofore been used as a typical material for an interlevel insulating film. The relative dielectric constant of a silicon dioxide film is, however, about 4 to about 4.5. Thus, it would be difficult to apply a silicon dioxide film to a semiconductor integrated circuit incorporating an even larger number of devices.
In order to solve such a problem, fluorine-doped silicon dioxide film, low-dielectric-constant spin-on-glass (SOG) film, organic polymer film and so on have been proposed as alternate interlevel insulating films with respective relative dielectric constants smaller than that of a silicon dioxide film.
The relative dielectric constant of a fluorine-doped silicon dioxide film is about 3.3 to about 3.7, which is about 20 percent lower than that of a conventional silicon dioxide film. Nevertheless, a fluorine-doped silicon dioxide film is highly hygroscopic, and easily absorbs water in the air, resulting in various problems in practice. For example, when the fluorine-doped silicon dioxide film absorbs water, SiOH groups, having a high relative dielectric constant, are introduced into the film. As a result, the relative dielectric constant of the fluorine-doped silicon dioxide film adversely increases, or the SiOH groups react with the water during a heat treatment to release H2O gas. In addition, fluorine free radicals, contained in the fluorine-doped silicon dioxide film, segregate near the surface thereof during a heat treatment and react with Ti, contained in a TiN layer formed thereon as an adhesion layer, to form a TiF film, which easily peels off.
An HSQ (hydrogen silsesquioxane) film, composed of Si, O and H atoms, is an exemplary low-dielectric-constant SOG film. In the HSQ film, the number of the H atoms is about two-thirds of that of the O atoms. However, the HSQ film releases a larger amount of water than a conventional silicon to dioxide film. Accordingly, since it is difficult to form buried interconnection in the HSQ film, a patterned metal film should be formed as metal interconnects on the HSQ film.
Also, since the HSQ film cannot adhere strongly to metal interconnects, a CVD oxide film should be formed between the metal interconnects and the HSO film to improve the adhesion therebetween. However, in such a case, if the CVD oxide film is formed on the metal interconnects, then the substantial line-to-line capacitance is equal to the serial capacitance formed by the HSQ and CVD films. This is because the CVD oxide film with a high dielectric constant exists between the metal interconnects. Accordingly, the resulting line-to-line capacitance is larger as compared with using the HSQ film alone.
An organic polymer film, as well as the low-dielectric constant SOG film, cannot adhere strongly to metal interconnects. Accordingly, a CVD oxide film should be formed as an adhesion layer between the metal interconnects and the organic polymer film, too.
Moreover, an etch rate, at which an organic polymer film is etched, is approximately equal to an ash rate, at which a resist pattern is ashed with oxygen plasma. Accordingly, a usual resist application process is not applicable in such a situation, because the organic polymer film is likely to be damaged during ashing and removing the resist pattern. Therefore, a proposed alternate process includes: forming a CVD oxide film on an organic polymer film; forming a resist film on the CVD oxide film; and then etching the resist film using the CVD oxide film as an etch stopper, or a protective film.
However, during the step of forming the CVD oxide film on the organic polymer film, the surface of the organic polymer film is exposed to a reactive gas containing oxygen. Accordingly, the organic polymer film reacts with oxygen to take in polar groups such as carbonyl groups and ketone groups. As a result, the relative dielectric constant of the organic polymer film disadvantageously increases.
Also, in forming inlaid copper interconnects in the organic polymer film, a TiN adhesion layer, for example, should be formed around wiring grooves formed in the organic polymer film, because the organic polymer film cannot adhere strongly to the metal interconnects. However, since the TiN film has a high resistance, the effective cross-sectional area of the metal interconnects decreases. Consequently, the intended effect attainable by the use of the copper lines, i.e., reduction in resistance, would be lost.
An object of the present invention is providing an interconnection structure, in which an interlevel insulating film with a low dielectric constant can be formed to adhere strongly to organic film, oxide film or metal film, and a method for forming the same.
A first interconnection structure according to the present invention includes an interlevel insulating film, made of organic-containing silicon dioxide, between lower- and upper-level metal interconnects. In the organic-containing silicon dioxide, a phenyl group, bonded to a silicon atom, is introduced into silicon dioxide.
In the first interconnection structure, a phenyl group, bonded to a silicon atom, is introduced into silicon dioxide in the organic-containing silicon dioxide as a material for the interlevel insulating film. Accordingly, such a film can be processed as well as a conventional CVD oxide film, has a relative dielectric constant as low as that of an HSQ film, and can adhere strongly to organic film, oxide film or metal film. Thus, the number of devices that can be integrated within a single semiconductor integrated circuit can be easily increased without modifying the conventional semiconductor device manufacturing process. As a result, a high-performance semiconductor integrated circuit, operative at a high speed and with lower power dissipation, is realized.
A second interconnection structure according to the present invention includes: lower-level metal interconnects; a first insulating film formed over the lower-level metal interconnects and mainly composed of organic-containing silicon dioxide, in which silicon dioxide contains an organic component; a second insulating film formed over the first insulating film and mainly composed of an organic component; upper-level metal interconnects formed in the second insulating film; and contacts formed in the first insulating film to interconnect the lower- and upper-level metal interconnects.
In the second interconnection structure, a first insulating film, mainly composed of organic-containing silicon dioxide, is formed under a second insulating film mainly composed of an organic component. Thus, in forming wiring grooves by etching the second insulating film using a resist pattern as a mask, the first insulating film, mainly composed of organic-containing silicon dioxide and having a low relative dielectric constant, functions as an etch stopper. That is to say, since a CVD oxide film with a high dielectric constant need not be formed as an etch stopper under the second insulating film, the relative dielectric constant of this interlevel insulating film can be lower than that of a conventional interlevel insulating film.
In one embodiment of the present invention, a phenyl group, bonded to a silicon atom, is preferably introduced into silicon dioxide in the organic-containing silicon dioxide.
In such an embodiment, the relative dielectric constant of the first insulating film can be further reduced and the adhesion between the first insulating film and the lower-level metal interconnects can be improved.
A third interconnection structure according to the present invention includes: metal interconnects; a first insulating film, which is formed over the metal interconnects to cover the metal interconnects and to leave grooves between the metal interconnects and is mainly composed of organic-containing silicon dioxide, in which silicon dioxide contains an organic component; a second insulating film, which is formed on the first insulating film to fill in the grooves and has a relative dielectric constant lower than that of the first insulating film; and a third insulating film, which is formed over the second insulating film and has a composition different from that of the second insulating film.
In the third interconnection structure, a first insulating film, mainly composed of organic-containing silicon dioxide adhering strongly to metal interconnects, is interposed between the metal interconnects and a second insulating film. Accordingly, there is no need to interpose a high-dielectric-constant adhesion layer between the metal interconnects and a second insulating film. Also, the first insulating film is formed over the metal interconnects to leave grooves therebetween and the second insulating film, having a relative dielectric constant lower than that of the first insulating film, is formed to fill in the grooves. That is to say, the second insulating film with a lower relative dielectric constant is interposed between the metal interconnects. As a result, the relative dielectric constant of the interlevel insulating film can be greatly lower than that of a conventional one.
In one embodiment of the present invention, the second insulating film is preferably mainly composed of an organic component, and the third insulating film is preferably mainly composed of organic-containing silicon dioxide, in which silicon dioxide contains an organic component.
In another embodiment of the present invention, a phenyl group, bonded to a silicon atom, is preferably introduced into silicon dioxide in the organic-containing silicon dioxide.
A first method for forming an interconnection structure according to the present invention includes the steps of: forming an interlevel insulating film out of organic-containing silicon dioxide over lower-level metal interconnects by a CVD process using a reactive gas containing phenyltrimethoxy silane, a phenyl group, bonded to a silicon atom, being introduced into silicon dioxide in the organic-containing silicon dioxide; forming wiring grooves and contact holes, communicating with the wiring grooves and exposing the lower-level metal interconnects, in the interlevel insulating film; and forming upper-level metal interconnects and contacts, interconnecting the lower- and upper-level metal interconnects together, by filling in the wiring grooves and the contact holes with a metal film.
In the first method for forming an interconnection structure, an organic-containing silicon dioxide film is formed by a CVD process using a reactive gas containing phenyltrimethoxy silane. Thus, an organic-containing silicon dioxide film, in which a phenyl group, bonded to a silicon atom, is introduced into silicon dioxide, can be formed with certainty. Accordingly, an interlevel insulating film, which can be processed as well as a conventional CVD oxide film, has a relative dielectric constant as low as that of an HSQ film, and can adhere strongly to organic film, oxide film or metal film, can be formed between the lower- and upper-level metal interconnects with certainty.
A second method for forming an interconnection structure according to the present invention includes the steps of: forming a first insulating film, mainly composed of organic-containing silicon dioxide, in which silicon dioxide contains an organic component, over lower-level metal interconnects; forming a second insulating film, mainly composed of an organic component, over the first insulating film; forming wiring grooves and contact holes, which communicate with the wiring grooves and expose the lower-level metal interconnects, by selectively etching the second and first insulating films, respectively; and forming upper-level metal interconnects and contacts, interconnecting the lower- and upper-level metal interconnects together, by filling in the wiring grooves and the contact holes with a metal film.
In the second method for forming an interconnection structure, a first insulating film, mainly composed of organic-containing silicon dioxide, in which silicon dioxide contains an organic component, is formed over lower-level metal interconnects, and then a second insulating film, mainly composed of an organic component, is formed over the first insulating film. Thus, in the step of forming wiring grooves by selectively etching the second insulating film, the first insulating film functions as an etch stopper. That is to say, since a CVD oxide film with a high dielectric constant need not be formed as an etch stopper under the second insulating film, the relative dielectric constant of this interlevel insulating film can be lower than that of a conventional one.
In one embodiment of the present invention, a phenyl group, bonded to a silicon atom, is preferably introduced into silicon dioxide in the organic-containing silicon dioxide.
In such an embodiment, the relative dielectric constant of the first insulating film can be further reduced and the adhesion between the first insulating film and the lower-level metal interconnects can be improved.
A third method for forming an interconnection structure according to the present invention includes the steps of: forming a first insulating film, mainly composed of organic-containing silicon dioxide, in which silicon dioxide contains an organic component, over metal interconnects to cover the metal interconnects and to leave grooves between the metal interconnects; forming a second insulating film, having a relative dielectric constant lower than that of the first insulating film, on the first insulating film to fill in the grooves; and forming a third insulating film, having a composition different from that of the second insulating film, over the second insulating film.
In the third method for forming an interconnection structure, a first insulating film, mainly composed of organic-containing silicon dioxide, is formed over metal interconnects to leave grooves therebetween, and then a second insulating film, having a lower relative dielectric constant, is formed over the first insulating film to fill in the grooves. Accordingly, there is no need to interpose a high-dielectric-constant adhesion layer between the metal lines and the second insulating film. Instead, the second insulating film with a low relative dielectric constant is interposed between the metal interconnects. As a result, the relative dielectric constant of the interlevel insulating film can be greatly lower than that of a conventional one.
In one embodiment of the present invention, the second insulating film is preferably mainly composed of an organic component, and the third insulating film is preferably mainly composed of organic-containing silicon dioxide, in which silicon dioxide contains an organic component.
In such an embodiment, a third insulating film, mainly composed of organic-containing silicon dioxide, is formed over a second insulating film mainly composed of an organic component. Accordingly, in the step of ashing and removing a resist pattern with plasma, it is possible to prevent the second insulating film from being damaged by the plasma.
In this case, a phenyl group, bonded to a silicon atom, is preferably introduced into silicon dioxide in the organic-containing silicon dioxide.
In such an embodiment, the relative dielectric constant of the third insulating film can be further reduced and the adhesion between the third insulating film and metal interconnects to be formed on the third insulating film can be improved.
A fourth method for forming an interconnection structure according to the present invention includes the steps of: forming a first insulating film over lower-level metal interconnects; forming a second insulating film, which has a different composition than that of the first insulating film and is mainly composed of an organic component, over the first insulating film; forming a conductive film on the second insulating film; forming a first resist pattern, having a plurality of openings for forming wiring grooves, on the conductive film; etching the conductive film using the first resist pattern as a mask, thereby forming a mask pattern out of the conductive film to have the openings for forming wiring grooves; forming a second resist pattern, having a plurality of openings for forming contact holes, over the first resist pattern; selectively etching the second insulating film, thereby patterning the second insulating film to have the openings for forming contact holes and removing the first and second resist patterns; etching the first insulating film using the patterned second insulating film as a mask, thereby forming contact holes in the first insulating film to expose the lower-level metal interconnects; etching the second insulating film using the mask pattern as a mask, thereby forming wiring grooves in the second insulating film; and filling in the wiring grooves and the contact holes with a metal film, thereby forming upper-level metal interconnects and contacts interconnecting the lower- and upper-level metal interconnects together.
In the fourth method for forming an interconnection structure, the composition of the first insulating film, in which the contact holes are formed, is different from that of the second insulating film in which the wiring grooves are formed. Accordingly, in forming the wiring grooves by etching the second insulating film using a mask pattern as a mask, the first insulating film functions as an etch stopper. As a result, the depth of the wiring grooves can be self-aligned with the thickness of the second insulating film. Also, since the second insulating film is mainly composed of an organic component, the first and second resist patterns are removed during the step of forming the openings for forming contact holes in the second insulating film by selectively etching the second insulating film. That is to say, there is no need to perform the step of ashing and removing the first and second resist patterns. As a result, it is possible to prevent the second insulating film, mainly composed of an organic component, from being damaged during an ashing process step.
In one embodiment of the present invention, the first insulating film is preferably mainly composed of organic-containing silicon dioxide, in which silicon dioxide contains an organic component.
In such an embodiment, there is no need to interpose a high-dielectric-constant adhesion layer between the metal interconnects and the second insulating film. As a result, the relative dielectric constant of the interlevel insulating film can be greatly lower than that of a conventional one.
In this case, a phenyl group, bonded to a silicon atom, is preferably introduced into silicon dioxide in the organic-containing silicon dioxide.
In such an embodiment, the relative dielectric constant of the first insulating film can be further reduced and the adhesion between the metal interconnects and the first insulating film can be improved.